Tree Core Analysis with X-ray Computed Tomography

Summary

Here we show how to process tree cores with an X-ray computed tomography toolchain. Except for chemical extraction for some purposes, no further physical lab treatment is needed. The toolchain can be used for biomass estimations, for obtaining MXD/tree-ring width data as well as for obtaining quantitative wood anatomy data.

Abstract

An X-ray computed tomography (CT) toolchain is presented to obtain tree-ring width (TRW), maximum latewood density (MXD), other density parameters, and quantitative wood anatomy (QWA) data without the need for labor-intensive surface treatment or any physical sample preparation. The focus here is on increment cores and scanning procedures at resolutions ranging from 60 µm down to 4 µm. Three scales are defined at which wood should be looked at: (i) inter-ring scale, (ii) ring scale, i.e., tree-ring analysis and densitometry scale, as well as (iii) anatomical scale, the latter approaching the conventional thin-section quality. Custom-designed sample holders for each of these scales enable high-throughput scanning of multiple increment cores. A series of software routines were specifically developed to efficiently treat three-dimensional X-ray CT images of the tree cores for TRW and densitometry. This work briefly explains the basic principles of CT, which are needed for a proper understanding of the protocol. The protocol is presented for some known species that are commonly used in dendrochronology. The combination of rough density estimates, TRW and MXD data, as well as quantitative anatomy data, allows us to broaden and deepen current analyses for climate reconstructions or tree response, as well as further develop the field of dendroecology/climatology and archeology.

Introduction

Wood density is an easy-to-measure variable¹ that reflects both the anatomical and chemical properties of the wood². In biomass estimations of aboveground biomass, wood density is an important weighing variable ^3,4,5, that is multiplied with the dimensions of the tree and a factor representing the carbon content of the wood. Wood density is tightly linked to the mechanical properties of timber⁶ and reflects the life history of a tree⁷.

Cell wall density ....

Protocol

1. Core sampling

1. Sample the tree with a Pressler borer. Consult references on how to core a tree manually³⁹. This toolchain is presented for 5.15 mm cores.
2. Put the tree cores unglued into 6 mm paper straws or in any other receptor that does not require glue. Do not glue the tree cores on a wooden support. If the cores were already mounted, unmount them with scalpel/saw or solvent depending on the glue type.
3. Avoid wrapping them in plastic tubes, try to dry them first to avoid mold growth and fungal decay.
4. Use pencil to write on the paper straws, since the extraction could fade marker wri....

Discussion

Critical steps within the protocol
Critical steps within the protocol include proper handling of the increment borer to obtain high-quality increment cores (step 1.1. and see³⁹) to avoid bits and pieces. Next, it is essential that cores be left unmounted (but see²⁶), both for insertion in the sample holder (Figure 5, see²¹) as well as for proper resin extraction⁵⁰ and for possible future ana.......

Materials

Name	Company	Catalog Number	Comments
6 mm paper straws	http://artstraws.com/education/product/artstraws-thick-asst-cols/		Coring
Aluminium core holders
ASTM standard ASTM D 1107 – 96
Cardboard postal tubes	https://www.rajapack.co.uk/envelopes-mailing-bags/postal-tubes/1-5-2mm-brown-cardboard-postal-tubes_PDT05623.html
Column drill
Computer hardware for reconstruction and analysis			X-ray CT scanning
Cooling
Drying oven
Ethanol
Flask for under soxhlet (2000 ml)
Floral foam	https://www.oasisfloral.eu/		Sample holder type 1
Glass beads to fill void volume of Soxhlet to save solvent
Glue
Hot water bath	https://www.memmert.com/products/water-baths/water-bath/#!filters=%7B%7D		Soxhlet extraction
Increment borer	https://haglofsweden.com/project/increment-borers/
Plastic cylinder	Moonen et al. 2022		Sample holder type 2
Plastic cylinders
Reservoir
Tailored soxhlet apparatus
Toluene
Water pump
X-ray CT scanner